Stretchable film laminate and electronic device

ABSTRACT

A stretchable film laminate that includes a laminated body and external electrodes. The laminated body is formed such that a plurality of stretchable films and a plurality of main-surface electrodes are laminated in an alternate manner. The stretchable films are provided with cuts through which some of the main-surface electrodes are partially exposed. The external electrodes are connected to a part of the main-surface electrodes exposed through the cuts.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International applicationNo. PCT/JP2015/073950, filed Aug. 26, 2015, which claims priority toJapanese Patent Application No. 2014-186376, filed Sep. 12, 2014, theentire contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a stretchable film laminate obtained bylaminating stretchable films that stretch in a planar direction throughthe application of a voltage, and an electronic device including thestretchable film laminate.

BACKGROUND OF THE INVENTION

Conventionally, many stretchable film laminates have been used which areobtained by laminating stretchable films that stretch in a planardirection through the application of a voltage. For example, PatentDocument 1 discloses a piezoelectric speaker 90 as shown in FIG. 10.

FIG. 10 is a cross-sectional view of the piezoelectric speaker 90according to Patent Document 1.

The piezoelectric speaker 90 includes a laminated body 2, a positiveelectrode 9 (first external electrode), a negative electrode 10 (secondexternal electrode), and a diaphragm 11.

The laminated body 2 is a cuboid. The laminated body 2 is formed suchthat first main-surface electrodes 5, film layers 1 (piezoelectricfilms), and second main-surface electrodes 6 are laminated in analternate manner. The film layers 1 are composed of a polylactic acid.The positive electrode 9 for the application of driving signals, whichis connected to the plurality of first main-surface electrodes 5, isprovided on one end surface of the laminated body 2.

In addition, the negative electrode 10 for the application of drivingsignals, which is connected to the plurality of second main-surfaceelectrodes 6, is provided on the other end surface of the laminated body2. The laminated body 2 is bonded to one principal surface of thediaphragm 11 with an adhesive layer 12 interposed therebetween.

In the foregoing configuration, when a driving voltage (driving signal)is applied to the laminated body 2 from the plurality of firstmain-surface electrodes 5 and the plurality of second main-surfaceelectrodes 6 through the positive electrode 9 and the negative electrode10, the laminated body 2 stretches, for example, in a planar directionperpendicular to the laminating direction, thereby vibrating thediaphragm 11. Thus, the piezoelectric speaker 90 emits a sound.

Patent Document 1: Japanese Patent Application Laid-Open No. 2014-68141

SUMMARY OF THE INVENTION

However, the piezoelectric speaker 90 in Patent Document 1 has a narrowconnection area between the first main-surface electrodes 5 and thepositive electrode 9. Likewise, the speaker has a narrow connection areabetween the second main-surface electrodes 6 and the negative electrode10.

Therefore, in the piezoelectric speaker 90 in Patent Document 1, theconnection strength is low between the first main-surface electrodes 5and the positive electrode 9 (first external electrode), and there is apossibility of causing defective bonding such as peeling between thefirst main-surface electrodes 5 and the positive electrode 9. Likewise,the connection strength is low between the second main-surfaceelectrodes 6 and the negative electrode 10 (second external electrode),and there is a possibility of causing defective bonding such as peelingbetween the second main-surface electrodes 6 and the negative electrode10.

Further, because of the narrow connection area between the firstmain-surface electrodes 5 and the positive electrode 9, long-termheating is required so as to ensure that both electrodes are reliablyconnected to each other. However, there is a possibility that the filmlayers 1 will be melted during this heating.

Therefore, an object of the present invention is to provide astretchable film laminate and an electronic device which can improve theconnection strength between a main-surface electrode and an externalelectrode.

A stretchable film laminate according to the present invention includesa laminated body formed by laminating: a first main-surface electrode; afirst stretchable film with a first main surface bonded to the firstmain-surface electrode and a second main surface opposed to the firstmain surface; a second main-surface electrode bonded to the second mainsurface of the first stretchable film; a second stretchable film with athird main surface bonded to the second main-surface electrode and afourth main surface opposed to the third main surface; and a thirdmain-surface electrode bonded to the fourth main surface of the secondstretchable film.

The first stretchable film and the second stretchable film are providedwith a first cut through which the third main-surface electrode ispartially exposed.

Further, the stretchable film laminate according to the presentinvention includes a first external electrode connected to a part of themain surface of the first main-surface electrode and a part of the mainsurface of the third main-surface electrode exposed through the firstcut.

In accordance with this configuration, the first external electrode canbe connected to the first and third main-surface electrodes on themain-surface side where a large area can be ensured. Accordingly, theconnection area between the first external electrode and the first andthird main-surface electrodes is larger than the connection area of thepiezoelectric speaker 90 in Patent Document 1.

Therefore, the stretchable film laminate in accordance with thisconfiguration can improve the connection strength between the firstexternal electrode and the first and third main-surface electrodes.

In addition, according to the present invention, the laminated body maybe, in one aspect, formed by further laminating: a third stretchablefilm with a fifth main surface bonded to the third main-surfaceelectrode and a sixth main surface opposed to the fifth main surface;and a fourth main-surface electrode bonded to the sixth main surface ofthe third stretchable film.

Further, the second stretchable film and the third stretchable film arepreferably provided with a second cut through which the secondmain-surface electrode is partially exposed. A second external electrodeis connected to a part of the main surface of the fourth main-surfaceelectrode and a part of the main surface of the second main-surfaceelectrode exposed through the second cut.

In accordance with this configuration, the second external electrode canbe connected to the second and fourth main-surface electrodes on themain-surface side where a large area can be ensured. Accordingly, inaccordance with this configuration, the connection area between thesecond external electrode and the second and fourth main-surfaceelectrodes is larger than the connection area of the piezoelectricspeaker 90 in Patent Document 1.

Therefore, the stretchable film laminate in accordance with thisconfiguration can further improve the connection strength between thesecond external electrode and the second and fourth main-surfaceelectrodes.

It is to be noted that in the foregoing configuration, when a drivingvoltage (driving signal) is applied to the laminated body through thefirst and second external electrodes from the first and thirdmain-surface electrodes and the second and fourth main-surfaceelectrodes, the laminated body stretches, for example, in the laminatingdirection.

In addition, the first external electrode or the second externalelectrode may be, in one aspect, stepped.

In addition, when the first cut or the second cut has a corner, thestretchable films are likely to be ruptured from the corner part in thestretching direction of the stretchable films, e.g., in the formation ofthe first cut or the second cut by punching of the stretchable filmswith a press mold. Therefore, the first cut or the second cut ispreferably curved.

In accordance with this configuration, the first cut or the second cuthas no corner, and can be thus prevented from being ruptured.

In addition, the stretchable films desirably have an electrostrictivematerial that stretches in a direction parallel to the main surfaceswhen an electric field is applied in a direction normal to the mainsurfaces, in particular, a (vinylidene fluoride-ethylenetrifluoride-chloroethene trifluoride) terpolymer P(VDF/TrFE/CTFE) or avinylidene fluoride-ethylene trifluoride copolymer P(VDF/TrFE) with ahigh electrostrictive coefficient. In addition, a polyvinylidenefluoride that stretches even in a low electric field can be also adoptedas a material, and a chiral polymer can be used as a material. Inparticular, when a chiral polymer is a polylactic acid, the adoption ofa light-transmitting material for the films, and also for the otherconfigurations, can achieve a stretchable film laminate that has ahighly light-transmitting property substantially over the entire surfacein a frontal view. The polylactic acid is preferably an L-typepolylactic acid.

In addition, an electronic device can be configured to include thestretchable film laminate according to the present invention. Therefore,the electronic device according to the present invention achievessimilar benefits to that of the stretchable film laminate according tothe present invention.

According to this invention, the connection strength can be improvedbetween the main-surface electrodes and the external electrodes.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a perspective view of the appearance of a stretchable filmlaminate 100 according to a first embodiment of the present invention.

FIG. 2 is a perspective view of the appearance of the stretchable filmlaminate 100 shown in FIG. 1.

FIG. 3 is a perspective view of the appearance of a laminated body 102shown in FIG. 1.

FIG. 4 is a perspective view of the appearance of the laminated body 102shown in FIG. 1.

FIG. 5 is a front view of the laminated body 102 shown in FIG. 1.

FIG. 6 is a perspective view of the appearance of a stretchable filmlaminate 200 according to a second embodiment of the present invention.

FIG. 7 is a cross-sectional view of a main part of a stretchable filmlaminate 300 according to a third embodiment of the present invention.

FIG. 8 is a perspective view of an interlayer connection part of astretchable film laminate 400 according to a fourth embodiment of thepresent invention.

FIG. 9 is a perspective view of the appearance of a keyboard 800according to another embodiment of the present invention.

FIG. 10 is a cross-sectional view of a piezoelectric speaker 90according to Patent Document 1.

DETAILED DESCRIPTION OF THE INVENTION

A stretchable film laminate according to a first embodiment of thepresent invention will be described with reference to the drawings.

FIG. 1 is a perspective view of the appearance of a stretchable filmlaminate 100 according to the first embodiment of the present invention.FIG. 2 is a perspective view of the appearance of the stretchable filmlaminate 100 shown in FIG. 1. FIG. 3 is a perspective view of theappearance of a laminated body 102 shown in FIG. 1. FIG. 4 is aperspective view of the appearance of the laminated body 102 shown inFIG. 1. FIG. 5 is a front view of the laminated body 102 shown in FIG.1.

It is to be noted that FIG. 1 is a view of the stretchable film laminate100 from a main-surface electrode 22 a (near side), whereas FIG. 2 is aview of the stretchable film laminate 100 from a main-surface electrode22 h (far side). FIG. 3 is a view of the stretchable film laminate 100with an external electrode 31 removed therefrom, whereas FIG. 4 is aview of the stretchable film laminate 100 with an external electrode 32removed therefrom.

The stretchable film laminate 100 includes the laminated body 102, theexternal electrode 31, and the external electrode 32.

It is to be noted that the external electrode 31 corresponds to thefirst external electrode. Further, the external electrode 32 correspondsto the second external electrode.

The laminated body 102 is short in the laminating direction, and has theshape of a cuboid. The laminated body 102 is formed such that aplurality of stretchable films 21 a to 21 g and a plurality ofmain-surface electrodes 22 a to 22 h are laminated in an alternatemanner.

The stretchable films 21 a to 21 g each stretch in a planar direction,for example, through the application of a voltage. For the stretchablefilms 21 a to 21 g, a (vinylidene fluoride-ethylenetrifluoride-chloroethene trifluoride) terpolymer P(VDF/TrFE/CTFE) or avinylidene fluoride-ethylene trifluoride copolymer P(VDF/TrFE) is usedas an electrostrictive material. In addition, a piezoelectric resinmaterial may be used such as polyvinylidene fluoride (PVDF) and chiralpolymers. The films composed of a highly light-transmitting polylacticacid (PLA), in particular, an L-type polylactic acid (PLLA), and theother configurations also made with the use of highly light-transmittingmaterials can achieve the stretchable film laminate 100 which has ahighly light-transmitting property substantially over the entire surfacein a frontal view.

When the stretchable films 21 a to 21 g are each composed of a PLLA,cutting the films such that each peripheral side makes substantially 45°with respect to the extending direction forms rectangular shapes withpiezoelectricity. In this regard, the term of substantially 45°represents 45°±10°.

It is to be noted that the PLLA without pyroelectricity is not affectedby the change in ambient temperature. Therefore, the vibration strengthis not changed by the change in temperature, heat generation of anelectronic device, temperature change by contact with a finger, or thelike.

The external electrodes 31, 32 are stepped as shown in FIGS. 1 and 2.Leads, not shown, are bonded with a solder respectively to the externalelectrodes 31, 32. The external electrodes 31, 32 are provided forstretching the stretchable film laminate 100, for example, in thelaminating direction through the application of a driving voltage to thestretchable film 21 through the main-surface electrode 22. The externalelectrodes 31, 32 are formed from Ag, Cu, Au, Cr, Ni, Al, or an alloy orthe like of these metals.

In addition, the main-surface electrode 22 of the laminated body 102 iscomposed of the plurality of main-surface electrodes 22 a to 22 h.

The main-surface electrodes 22 a, 22 c, 22 e, 22 g each have one endconnected to the external electrode 31. The main-surface electrodes 22a, 22 c, 22 e, 22 g extend horizontally (in a direction perpendicular tothe laminating direction) from the external electrode 31 toward theexternal electrode 32.

In this regard, the widthwise length of the laminated body 102 at themain-surface electrodes 22 a, 22 c, 22 e, 22 g is shorter than thelength from a side surface of the laminated body 102 closer to theexternal electrode 32, to the external electrode 31. Therefore, themain-surface electrodes 22 a, 22 c, 22 e, 22 g are not connected to theexternal electrode 32.

It is to be noted that the main-surface electrode 22 a corresponds tothe first main-surface electrode. The main-surface electrodes 22 c, 22 ecorrespond to the first main-surface electrode or the third main-surfaceelectrode. The main-surface electrode 22 g corresponds to the thirdmain-surface electrode.

The main-surface electrodes 22 b, 22 d, 22 f are located between themain-surface electrodes 22 a and 22 c, between the main-surfaceelectrodes 22 c and 22 e, and between the main-surface electrodes 22 eand 22 g, respectively. The main-surface electrodes 22 b, 22 d, 22 f, 22h each have one end connected to the external electrode 32. Themain-surface electrodes 22 b, 22 d, 22 f, 22 h extend horizontally (in adirection perpendicular to the laminating direction) from the externalelectrode 32 toward the external electrode 31.

In this regard, the widthwise length of the laminated body 102 at themain-surface electrodes 22 b, 22 d, 22 f, 22 h is shorter than thelength from a side surface of the laminated body 102 closer to theexternal electrode 31, to the external electrode 32. Therefore, themain-surface electrodes 22 b, 22 d, 22 f, 22 h are not connected to theexternal electrode 31.

It is to be noted that the main-surface electrode 22 b corresponds tothe second main-surface electrode. The main-surface electrodes 22 d, 22f correspond to the second main-surface electrode or the fourthmain-surface electrode. The main-surface electrode 22 h corresponds tothe fourth main-surface electrode.

The main-surface electrode 22 is formed from, for example, Ag, Cu, Au,Cr, Ni, Al, or an alloy or the like of these metals.

In this regard, as shown in FIG. 3, the stretchable films 21 a, 21 b areprovided with a cut 25 through which the main-surface electrode 22 c ispartially exposed. The stretchable films 21 c, 21 d are provided with acut 26 through which the main-surface electrode 22 e is partiallyexposed.

In addition, the stretchable films 21 e, 21 f are provided with a cut 27through which the main-surface electrode 22 g is partially exposed.

It is to be noted to the cuts 25 to 27 correspond to the first cutaccording to the present invention.

In addition, as shown in FIG. 4, the stretchable films 21 g, 21 f areprovided with a cut 77 through which the main-surface electrode 22 f ispartially exposed. The stretchable films 21 e, 21 d are provided with acut 76 through which the main-surface electrode 22 d is partiallyexposed.

The stretchable films 21 c, 21 b are provided with a cut 75 throughwhich the main-surface electrode 22 b is partially exposed.

It is to be noted that the cuts 75 to 77 correspond to the second cutaccording to the present invention.

Further, as shown in FIG. 1, the external electrode 31 is connected to apart of the main surface of the main-surface electrode 22 a and parts ofthe main surfaces of the main-surface electrodes 22 c, 22 e, 22 gexposed through the cuts 25 to 27. In addition, as shown in FIG. 2, theexternal electrode 32 is connected to a part of the main surface of themain-surface electrode 22 h and parts of the main surfaces of themain-surface electrodes 22 f, 22 d, 22 b exposed through the cuts 75 to77.

Therefore, in the stretchable film laminate 100, the external electrode31 can be connected to the main-surface electrodes 22 a, 22 c, 22 e, 22g on the main-surface side where a large area can be ensured.Accordingly, the connection area between the external electrode 31 andthe main-surface electrodes 22 a, 22 c, 22 e, 22 g is larger than theconnection area of the piezoelectric speaker 90 in Patent Document 1.

Likewise, in the stretchable film laminate 100, the external electrode32 can be connected to the main-surface electrodes 22 h, 22 f, 22 d, 22b on the main-surface side where a large area can be ensured. Therefore,the connection area between the external electrode 32 and themain-surface electrodes 22 h, 22 f, 22 d, 22 b is larger than theconnection area of the piezoelectric speaker 90 in Patent Document 1.

Therefore, the stretchable film laminate 100 can improve the connectionstrength between the external electrode 31 and the main-surfaceelectrodes 22 a, 22 c, 22 e, 22 g. Furthermore, the stretchable filmlaminate 100 can improve the connection strength between the externalelectrode 32 and the main-surface electrodes 22 h, 22 f, 22 d, 22 b.

In accordance with the foregoing configuration, when analternating-current driving voltage (driving signal) is applied from theleads bonded to the external electrodes 31, 32, the driving voltage isapplied to the laminated body 102 from the main-surface electrodes 22 a,22 c, 22 e, 22 g and the main-surface electrodes 22 b, 22 d, 22 f, 22 hthrough the external electrodes 31, 32.

Thus, the laminated body 102 stretches, for example, in the laminatingdirection.

It is to be noted that in the stretchable film laminate 100, as shown inFIG. 5, the region 28 can be effectively used by forming the cut 25 soas to meet L₀>L₁ and D₀>D₁ when the vertical length of the stretchablefilm 21 a is denoted by L₀, the vertical length of the cut 25 is denotedby L₁, the horizontal length of the stretchable film 21 a is denoted byD₀, and the horizontal length of the cut 25 is denoted by D₁.

In addition, in the stretchable film laminate 100, the shapes and areasof the exposed parts of the main-surface electrodes 22 c, 22 e, 22 g canbe changed by changing the shapes of the cuts 25 to 27. Likewise, theshapes and areas of the exposed parts of the main-surface electrodes 22f, 22 d, 22 b can be changed by changing the shapes of the cuts 75 to77.

In addition, the connections are achieved, but not limited thereto, withthe external electrode 31 and the external electrode 32 in the firstembodiment. External electrodes may be provided in multiple locations.

Next, a stretchable film laminate 200 according to a second embodimentof the present invention will be described below.

FIG. 6 is a perspective view of the appearance of the stretchable filmlaminate 200 according to the second embodiment of the presentinvention. The differences of the stretchable film laminate 200 from thestretchable film laminate 100 described previously are mainly the shapesof stretchable films 221 a to 221 g.

The stretchable films 221 a to 221 g have cuts 225 to 227 in curvedshapes. The other configurations of the stretchable films 221 a to 221 gare the same as those of the stretchable films 21 a to 21 g, and theexplanations thereof will be thus left out.

The main-surface electrode 222 of a laminated body 202 is composed ofthe plurality of main-surface electrodes 222 a to 222 h. Themain-surface electrodes 222 a to 222 h have shape respectively inaccordance with the stretchable films 221 a to 221 g.

More specifically, the main-surface electrodes 222 a, 222 c, 222 e, 222g are connected to a first external electrode 231. The main-surfaceelectrodes 222 a, 222 c, 222 e, 222 g are not connected to a secondexternal electrode, not shown. In this regard, the first externalelectrode 231 and the second external electrode have the same materialas the first external electrode 31.

In addition, the main-surface electrodes 222 b 222 d, 222 f are locatedbetween the main-surface electrodes 222 a and 222 c, between themain-surface electrodes 222 c and 222 e, and between the main-surfaceelectrodes 222 e and 222 g, respectively. The main-surface electrodes222 b, 222 d, 222 f, 222 h are connected to the second externalelectrode, not shown. The main-surface electrodes 222 b, 222 d, 222 f,222 h are not connected to the first external electrode 231.

The other main-surface electrodes 222 a to 222 h have the sameconfigurations as the main-surface electrodes 22 a to 22 h, and theexplanations thereof will be thus left out.

It is to be noted that the main-surface electrode 222 a corresponds tothe first main-surface electrode. The main-surface electrodes 222 c, 222e correspond to the first main-surface electrode or the thirdmain-surface electrode. The main-surface electrode 222 g corresponds tothe third main-surface electrode.

Further, the external electrode 231 is connected to a part of the mainsurface of the main-surface electrode 222 a and parts of the mainsurfaces of the main-surface electrodes 222 c, 222 e, 222 g exposedthrough the cuts 225 to 227.

In the foregoing configuration, in the stretchable film laminate 200,the first external electrode 231 can be connected to the main-surfaceelectrodes 222 a, 222 c, 222 e, 222 g on the main-surface side where alarge area can be ensured. Therefore, the connection area between thefirst external electrode 231 and the main-surface electrodes 222 a, 222c, 222 e, 222 g is larger than the connection area of the piezoelectricspeaker 90 in Patent Document 1.

Therefore, the stretchable film laminate 200 can improve the connectionstrength between the first external electrode 231 and the main-surfaceelectrodes 222 a, 222 c, 222 e, 222 g, as with the stretchable filmlaminate 100.

In this regard, as shown in FIGS. 1 to 5, the stretchable films 21 a to21 g are, because of the cuts 25 to 27, 75 to 77 with corners, likely tobe ruptured from the corner parts in the stretching direction of thestretchable films 21 a to 21 g.

On the other hand, the stretchable film laminate 200 has the cuts 225 to227 without any corner. Therefore, the stretchable film laminate 200 canprevent the stretchable films 221 a to 221 g from being ruptured.

Next, a stretchable film laminate 300 according to a third embodiment ofthe present invention will be described below.

FIG. 7 is a cross-sectional view of a main part of a stretchable filmlaminate 300 according to a third embodiment of the present invention.

The differences of the stretchable film laminate 300 from thestretchable film laminate 100 described previously are mainly the endshapes of stretchable films 321 a to 321 j and the shape of a firstexternal electrode 331.

The stretchable films 321 a to 321 d are provided with cuts 325, 326such that the stretchable films 321 a to 321 f have respective ends in astepwise manner. Main-surface electrodes 322 e, 322 i are partiallyexposed through the cuts 325, 326.

Furthermore, the stretchable films 321 g to 321 j are provided with cuts327, 328 such that the stretchable films 321 e to 321 j have respectiveends in a stepwise manner. Main-surface electrodes 322 l, 322 p arepartially exposed through the cuts 327, 328.

The other stretchable films 321 a to 321 j have the same configurationsas the stretchable films 21 a to 21 g, and the explanations thereof willbe thus left out.

In addition, the main-surface electrode 322 of a laminated body 302 iscomposed of a plurality of main-surface electrodes 322 a to 322 t. Themain-surface electrodes 322 a to 322 t have shape respectively inaccordance with the stretchable films 321 a to 321 j.

The main-surface electrodes 322 d, 322 h, 322 m, 322 q are bonded to themain-surface electrodes 322 e, 322 i, 3221, 322 p, respectively.Further, the main-surface electrodes 322 a, 322 d, 322 e, 322 h, 322 i,3221, 322 m, 322 p, 322 q, 322 t are connected to a first externalelectrode 331.

On the other hand, the main-surface electrodes 322 a, 322 d, 322 e, 322h, 322 i, 3221, 322 m, 322 p, 322 q, 322 t are not connected to a secondexternal electrode, not shown. In this regard, the first externalelectrode 331 and the second external electrode have the same materialas the first external electrode 31.

In addition, the main-surface electrodes 322 b, 322 c, 322 f, 322 g, 322j, 322 k, 322 n, 322 o, 322 r, 322 s are located between themain-surface electrodes 322 a and 322 d, between the main-surfaceelectrodes 322 e and 322 h, between the main-surface electrodes 322 iand 322 l, between the main-surface electrodes 322 m and 322 p, andbetween the main-surface electrodes 322 q and 322 t, respectively.

The main-surface electrodes 322 b, 322 c, 322 f, 322 g, 322 j, 322 k,322 n, 322 o, 322 r, 322 s are connected to the second externalelectrode, not shown. The main-surface electrodes 322 b, 322 c, 322 f,322 g, 322 j, 322 k, 322 n, 322 o, 322 r, 322 s are not connected to thefirst external electrode 331.

The other main-surface electrodes 322 a to 322 t have the sameconfigurations as the main-surface electrodes 22 a to 22 h, and theexplanations thereof will be thus left out.

It is to be noted that the main-surface electrodes 322 a, 322 tcorresponds to the first main-surface electrodes. The main-surfaceelectrodes 322 e, 322 p correspond to the first main-surface electrodeor the third main-surface electrode. The main-surface electrode 322 i,3221 correspond to the third main-surface electrodes.

Further, the first external electrode 331 is connected to parts of themain surfaces of the main-surface electrodes 322 a, 322 t and parts ofthe main surfaces of the main-surface electrodes 322 e, 322 i, 3221, 322p exposed through the cuts 325 to 328.

In the foregoing configuration, in the stretchable film laminate 300,the first external electrode 331 can be connected to the main-surfaceelectrodes 322 a, 322 e, 322 i, 3221, 322 p, 322 t on the main-surfaceside where a large area can be ensured. Therefore, in the stretchablefilm laminate 300, the connection area between the external electrode331 and the main-surface electrodes 322 a, 322 e, 322 i, 3221, 322 p,322 t is larger than the connection area of the piezoelectric speaker 90in Patent Document 1.

Furthermore, in the stretchable film laminate 300, the first externalelectrode 331 sandwiches, from both sides, parts of the main surfaces ofthe main-surface electrodes 322 a, 322 e, 322 i, 3221, 322 p, 322 t.

Therefore, the stretchable film laminate 300 can further improve theconnection strength between the first external electrode 331 and themain-surface electrodes 322 a, 322 e, 322 i, 3221, 322 p, 322 t.

Furthermore, as shown in FIG. 7, the first external electrode 331sandwiches the parts from the both sides, thereby making it possible forthe stretchable film laminate 300 to suppress warpage of the stretchablefilms 321 a to 321 j.

Next, a stretchable film laminate 400 according to a fourth embodimentof the present invention will be described below.

FIG. 8 is a perspective view of an interlayer connection part of thestretchable film laminate 400 according to the fourth embodiment of thepresent invention. The stretchable films 21 a to 21 g, main-surfaceelectrode 22, and external electrode 31 provided for the stretchablefilm laminate 400 are the same as those of the stretchable film laminate100 according to the first embodiment. The stretchable film laminate 400is characterized by being fixed with the overlapped external electrode31 and grommets 451 to 454, for each exposed part of the respectivelayers of the stretchable films 21 a to 21 g.

The stretchable film laminate 400 has the foregoing structure, and canthus firmly fix the external electrode 31 and the laminated body 102. Inaddition, the stretchable film laminate 400 can firmly press thecontacts between the stretchable films 21 a to 21 g and the externalelectrode 31. This fixing method is an effective connecting method forresin films where it is not possible to use baked electrodes orthermosetting conductive adhesives because of low heat resistance. Inaddition, the stretchable film laminate 400 has connection made on themain-surface side, unlike structures with connection made at sidesurfaces as in the cited Document 1 mentioned previously, and thus canuse connection methods such as grommets.

It is to be noted that while the exposed electrodes of the respectivelayers are each fixed to the external electrode with the grommets in thepresent embodiment, the two layers adjacent to each other may be fixedwith one grommet. In addition, swaging terminals may be used instead ofthe grommets, and multiple layers may be swaged together.

In addition, in the respective embodiments described previously, thestretchable films can be composed of, for example, piezoelectric films,electrostrictive films, electret films, piezoelectric ceramics,composite films with piezoelectric particles dispersed in polymers,electroactive polymer films, or the like.

In this regard, the electroactive polymer film is a film that produce astress by electrical drive, or a film that deforms and then producesdisplacement by electrical drive. Specifically, there areelectrostrictive films, composite materials (materials of piezoelectricceramics sealed with resin), electrically driven elastomers, or liquidcrystal elastomers.

In addition, as described previously, the stretchable film laminates 100to 400 have high connection reliability. Therefore, for example, asshown in FIG. 9, the stretchable film laminate 100 can be applied to anelectronic device such as a keyboard 800. The keyboard 800 includes acontrol unit 811, a drive unit 812, a diaphragm 821, the stretchablefilm laminate 100, and a touch panel 830.

As shown in FIG. 9, the diaphragm 821, the stretchable film laminate100, and the touch panel 830 are laminated in the thickness direction.The diaphragm 821 is bonded at both ends with an adhesive to both endsof the stretchable film laminate 100. Tension propagates to thediaphragm 821 from the stretchable film laminate 100, and the diaphragm821 undergoes elastic deformation so as to undergo a deflection in thethickness direction.

The touch panel 830 is bonded with an adhesive to the top surface of thediaphragm 821. The touch panel 830 includes a plurality of touch sensors831 exposed at top surface of the keyboard 800. The plurality of touchsensors 831 is disposed in positions corresponding to the keyarrangement of the keyboard.

Each touch sensor 831 outputs, in response to the detection of a touchpanel operation carried out by a user, the detection signal to thecontrol unit 811. The control unit 811 outputs a control signal to thedrive unit 812 when the detection signal is input from any of the touchsensors 831. The drive unit 812 applies a driving voltage to thestretchable film laminate 100 when a control signal is input from thecontrol unit 811.

When an alternating-current driving voltage (driving signal) is appliedfrom the leads bonded to the external electrodes 31, 32, the drivingvoltage is applied to the laminated body 102 from the main-surfaceelectrodes 22 a, 22 c, 22 e, 22 g and the main-surface electrodes 22 b,22 d, 22 f, 22 h through the external electrodes 31, 32. Thus, thestretchable film laminate 100 stretches, for example, in a planardirection. The diaphragm 821 vibrates with stretching of the stretchablefilm laminate 100.

Therefore, the keyboard 800 can provide a tactile feedback to users thatcarry out touch panel operations. It is to be noted that the keyboard800 may include each of the stretchable film laminates 200 to 400, inplace of the stretchable film laminate 100.

Finally, the descriptions of the respective embodiments should beconsidered by way of examples in all respects, but non-limiting. Thescope of the present invention is specified by the claims, but not theembodiments described above. Furthermore, the scope of the presentinvention is intended to encompass all modifications within the spiritand scope equivalent to the claims.

DESCRIPTION OF REFERENCE SYMBOLS

-   -   1: film layer    -   2: laminated body    -   5: first main-surface electrode    -   6: second main-surface electrode    -   9: positive electrode    -   10: negative electrode    -   11: diaphragm    -   12: adhesive layer    -   21 a to 21 g: stretchable film    -   22: main-surface electrode    -   26: region    -   31: first external electrode    -   32: second external electrode    -   90: piezoelectric speaker    -   100: stretchable film laminate    -   102: laminated body    -   200: stretchable film laminate    -   202: laminated body    -   221 a to 221 g: stretchable film    -   222: main-surface electrode    -   231: first external electrode    -   300: stretchable film laminate    -   302: laminated body    -   321 a to 321 j: stretchable film    -   322: main-surface electrode    -   331: first external electrode    -   400: stretchable film laminate    -   451 to 454: grommet    -   800: keyboard    -   811: control unit    -   812: drive unit    -   821: diaphragm    -   830: touch panel    -   831: touch sensor

1. A stretchable film laminate comprising: a laminated body having: afirst main-surface electrode; a first stretchable film having a firstmain surface thereof bonded to the first main-surface electrode and asecond main surface opposed to the first main surface; a secondmain-surface electrode bonded to the second main surface of the firststretchable film; a second stretchable film with a third main surfacebonded to the second main-surface electrode and a fourth main surfaceopposed to the third main surface; and a third main-surface electrodebonded to the fourth main surface of the second stretchable film, thefirst stretchable film and the second stretchable film having a firstcut through which the third main-surface electrode is exposed; and afirst external electrode connected to the first main-surface electrodeand the third main-surface electrode exposed through the first cut. 2.The stretchable film laminate according to claim 1, wherein the firstexternal electrode is stepped.
 3. The stretchable film laminateaccording to claim 1, wherein the first cut is curved.
 4. Thestretchable film laminate according to claim 1, wherein the laminatedbody further includes: a third stretchable film with a fifth mainsurface bonded to the third main-surface electrode and a sixth mainsurface opposed to the fifth main surface; and a fourth main-surfaceelectrode bonded to the sixth main surface of the third stretchablefilm, the second stretchable film and the third stretchable film havinga second cut through which the second main-surface electrode is exposed,and the laminate further comprises a second external electrode connectedto the fourth main-surface electrode and the second main-surfaceelectrode exposed through the second cut.
 5. The stretchable filmlaminate according to claim 4, wherein one of the first externalelectrode and the second external electrode is stepped.
 6. Thestretchable film laminate according claim 4, wherein one of the firstcut and the second cut is curved.
 7. The stretchable film laminateaccording to claim 4, wherein the first through fourth main-surfaceelectrodes and surfaces of any one of the first external electrode andthe second external electrode in contact therewith include throughholes, and the through holes are reinforced with swaged metal terminalsor grommets.
 8. The stretchable film laminate according to claim 1,wherein the first and second stretchable films are electrostrictive orpiezoelectric stretchable films.
 9. The stretchable film laminateaccording to claim 8, wherein the electrostrictive or piezoelectricstretchable films comprise a material selected from the group consistingof a vinylidene fluoride-ethylene trifluoride-chloroethene trifluorideterpolymer, a vinylidene fluoride-ethylene trifluoride copolymer, and apolyvinylidene fluoride that stretches more in a low electric field. 10.The stretchable film laminate according to claim 8, wherein theelectrostrictive or piezoelectric stretchable films comprise a chiralpolymer.
 11. The stretchable film laminate according to claim 10,wherein the chiral polymer is a polylactic acid.
 12. The stretchablefilm laminate according to claim 11, wherein the polylactic acid is anL-type polylactic acid.
 13. The stretchable film laminate according toclaim 4, wherein the first through third stretchable films areelectrostrictive or piezoelectric stretchable films.
 14. The stretchablefilm laminate according to claim 13, wherein the electrostrictive orpiezoelectric stretchable films comprise a material selected from thegroup consisting of a vinylidene fluoride-ethylenetrifluoride-chloroethene trifluoride terpolymer, a vinylidenefluoride-ethylene trifluoride copolymer, and a polyvinylidene fluoridethat stretches more in a low electric field.
 15. The stretchable filmlaminate according to claim 13, wherein the electrostrictive orpiezoelectric stretchable films comprise a chiral polymer.
 16. Thestretchable film laminate according to claim 15, wherein the chiralpolymer is a polylactic acid.
 17. The stretchable film laminateaccording to claim 16, wherein the polylactic acid is an L-typepolylactic acid.
 18. An electronic device comprising: the stretchablefilm laminate according to claim 1; and a drive unit that applies adriving voltage to the stretchable film laminate.